1. Field of the Invention
The present invention relates to composite high frequency components and mobile communication apparatuses incorporating the same. More particularly, the invention relates to composite high frequency components usable in a plurality of different mobile communication systems, and mobile communication apparatuses incorporating the same.
2. Description of the Related Art
Currently, in Europe, as mobile communication apparatuses, dual-band mobile telephones are provided. Such an apparatus can be operated in a plurality of communication systems using different frequency bands, for example, in a combination of the Digital Cellular System (DCS) using the 1.8 GHz band and the Global System for Mobile Communications (GSM) using 900 MHZ.
FIG. 10 shows a block diagram of a part of the structure of a conventional dual-band mobile telephone. It is an example in which the DCS using the 1.8 GHz band and the GSM using the 900 MHZ band are combined. The dual-band mobile telephone has an antenna 1, a diplexer 2, and two signal paths DCS and GSM.
The diplexer 2 selects signals transmitted from the DCS and the GSM at the time of transmission, and selects signals received in the DCS and the GSM at the time of reception. The DCS side is constituted of a high frequency switch 3a dividing the signal path into a transmission section Txd and a reception section Rxd, a high frequency filter 3b attenuating second-order harmonic signals and third-order harmonic signals on the DCS side, and a surface acoustic wave filter 3c preventing entering of the transmitted signals into the reception section Rxd. The GSM side is constituted of a high frequency switch 4a dividing the signal path into a transmission section Txg and a reception section Rxg, a high frequency filter 4b attenuating third-order harmonic signals on the GSM side, and a surface acoustic wave filter 4c preventing entering of the transmitted signals into the reception section Rxg.
Now, a description will be given of the operation of the dual-band mobile telephone by using the example of the DCS side. When a signal is transmitted, the high, frequency switch 3a makes a circuit to the transmission section Txd to send the signal transmitted from the transmission section Txd to the high frequency filter 3b. The diplexer 2 selects the signal passed through the high frequency filter 3b to transmit from the antenna 1. When a signal is received, the signal received in the antenna 1 is selected by the diplexer 2 to be sent to the high frequency filter 3b. The high frequency switch 3a makes a circuit to the reception section Rxd to send the signal passed through the high frequency filter 3b to the reception section Rxd via the surface acoustic wave filter 3c. In the GSM side, signals are also transmitted and received by the same operation.
However, in the conventional dual-band mobile telephone, the antenna, the diplexer, the high frequency switches in the DCS and the GSM sides, the high frequency filters, and the surface acoustic wave filters are independently mounted on a circuit board. As a result, in order to obtain matching characteristics, attenuation characteristics, and isolation characteristics, it is necessary to add matching circuits between the diplexer and the high frequency switches, between the high frequency switches and the high frequency filters, and between the high frequency switches and the surface acoustic wave filters, respectively. Thus, since the number of components and the area required for disposing the components are increased, the size of the circuit board is also increased. This leads to an increase in the size of the dual-band mobile telephone.
In order to solve the above problems, the present invention provides a composite high frequency component in which no matching circuits are necessary and a circuit board for mounting components can be miniaturized, and a mobile communication apparatus incorporating the same.
According to a first aspect of the present invention, there is provided a composite high frequency component included in a microwave circuit having a plurality of signal paths corresponding to respective frequencies. The composite high frequency component includes a diplexer which accepts signals transmitted from the corresponding plurality of single paths at a time of transmission, and delivers received signals to the plurality of signal paths at a time of reception; a plurality of high frequency switches dividing the plurality of signal paths into respective transmission sections and reception sections; a plurality of high frequency filters connected in respective signal paths; a plurality of surface acoustic wave filters connected to the reception-section sides at the rear of the corresponding plurality of high frequency switches; and a multi-layer substrate formed by laminating a plurality of ceramic sheet layers to integrate the diplexer, the high frequency switches, the high frequency filters, and the surface acoustic wave filters.
In addition, in the composite high frequency component, the plurality of high frequency filters may be connected to the transmission-section sides either at the front or at the rear of the corresponding plurality of high frequency switches.
In addition, in the composite high frequency component, the plurality of high frequency filters may be notch filters.
Furthermore, the above composite high frequency component may further include first inductance elements and first capacitance elements to form the diplexer; switching elements, second inductance elements, and second capacitance elements to form each of the plurality of high frequency switches; and a third inductance element and third capacitance elements to form each of the plurality of high frequency filters. In addition, the composite high frequency component may further include connecting sections formed inside the multi-layer substrate to connect the surface acoustic wave filters, the switching elements, the first to third inductance elements, and the first to third capacitance elements, some of which are contained in the multi-layer substrate and the remaining constituents are mounted thereon.
In this composite high frequency component, the surface acoustic wave filters may be mounted and sealed in a cavity formed inside the multi-layer substrate.
According to a second aspect of the present invention, there is provided a mobile communication apparatus including an antenna, a transmission section, a reception section, and the composite high frequency component described above.
In the above composite high frequency component, since the diplexer, the high frequency switches, the high frequency filters, and the surface acoustic wave filters constituting the composite high frequency component are integrated by the multi-layer substrate formed by laminating the plurality of ceramic sheet layers, connections between these constituents can be disposed inside the multi-layer substrate.
As a result, matching adjustments can be easily made, by techniques well known to those ordinarily skilled in the art, between the diplexer and the high frequency switches, between the high frequency switches and the high frequency filters, and between the high frequency switches and the surface acoustic wave filters. Thus, it is unnecessary to dispose matching circuits between the constituents.
Furthermore, since the mobile communication apparatus uses the composite high frequency component requiring no such matching circuits, the circuit board, on which the microwave circuit having the plurality of signal paths is formed, can be miniaturized.